Sheet feeding apparatus, image forming apparatus, and image reading apparatus

ABSTRACT

A sheet feeding apparatus includes a stacking member configured to be rotatably provided and to stack a sheet, a feeding member configured to feed the sheet by rotating in a state of coming in contact with the sheet stacked on the stacking member, an elastic member configured to generate a pressing force to make the sheet stacked on the stacking member come in contact with the feeding member, and a restricting unit configured to abut on an uppermost sheet stacked on the stacking member and to restrict a position of the uppermost sheet to a position separated from the feeding member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus which feeds astacked sheet, an image forming apparatus which includes the sheetfeeding apparatus, and an image reading apparatus which includes thesheet feeding apparatus.

2. Description of the Related Art

Conventionally, in an image forming apparatus such as a printer, acopying machine, and a facsimile machine, and an image reading apparatussuch as a scanner, there is provided a sheet feeding apparatus to feed asheet such as a recording target sheet or a sheet such as a readingtarget original to an image forming portion or an image reading portion.

Then, the image forming apparatus sequentially feeds the sheets stackedin a sheet cassette to the image forming portion by the sheet feedingapparatus, and forms an image on the sheet in the image forming portion.In addition, the image reading apparatus sequentially feeds theoriginals stacked on an original base plate by the sheet feedingapparatus to the image reading portion, and reads an original image inthe image reading portion.

Herein, for example, the sheet feeding apparatus provided in the imageforming apparatus may include a sheet supporting plate which isrotatable (movable) in a vertical direction (a direction of stackingsheet) and a feeding roller which feeds the sheets stacked on the sheetsupporting plate. The sheet feeding apparatus is configured such thatthe uppermost sheet of the sheet supporting plate is pressed toward thefeeding roller by a biasing member such as a spring, and in this state,the feeding roller is rotated to feed the uppermost sheet toward theimage forming portion.

However, in this sheet feeding apparatus, in a case where the sheet isleft under pressure of the feeding roller after a feeding operation iscompleted and then the sheet is fed, a plurality of sheets may besimultaneously fed to the image forming portion due to adsorptiongenerated between the sheets. Therefore, in order to prevent that thesheets are fed in an overlapping manner, when the feeding operation iscompleted, the sheet supporting plate is separated from the feedingroller at a predetermined position by a lift mechanism configured by acam or a motor.

However, in this sheet feeding apparatus, since the sheet supportingplate falls down to a certain position regardless of an amount ofstacked sheets so as to separate the sheet supporting plate from thefeeding roller, when the amount of stacked sheets is less, a gap betweenthe uppermost sheet stacked on the sheet supporting plate and thefeeding roller becomes wide compared to a large amount of sheets. Inthis way, in a case where the gap between the uppermost sheet and thefeeding roller stacked on the sheet supporting plate becomes wide, whenthe feeding operation is performed on the next sheet, a moving amount ofthe sheet supporting plate is increased, and a large time loss is causedwhen the sheet supporting plate is pressed by a roller for feeding thesheet. In addition, since the moving amount of the sheet supportingplate becomes large, kinetic energy generated when the sheet supportingplate makes the sheet abut on the feeding roller becomes large, so thatthere is a problem in that a larger collision noise is generated.

Therefore, there is proposed a technology in which the sheet supportingplate is moved to make the sheet pressed by the feeding roller when thesheet is fed, and a feeding motor is reversely rotated when the feedingoperation is completed, so that the sheet supporting plate is retractedfrom the feeding roller with respect to a press spring (see JapanesePatent No. 2601532). According to Japanese Patent No. 2601532, it ispossible to separate the stacked uppermost sheet from the feeding rollerto set a constant distance therebetween regardless of the amount ofstacked sheets.

Japanese Patent Laid-Open No. 2008-68949 discloses a configuration inwhich after the sheet is fed, a moving portion (which is movable) ismoved down to a position where a biasing force of the press spring ofthe sheet supporting plate is reduced, the sheet supporting plate ismoved by the weight of the stacked sheets against the biasing force ofthe press spring, and thus the sheet is separated from a sheet feedingportion. According to Japanese Patent Laid-Open No. 2008-68949, sincethe weight of the sheet supporting plate is changed according to theamount of stacked sheets, a separating amount of the sheet supportingplate varies to keep a constant distance between the stacked uppermostsheet and the feeding roller.

However, in Japanese Patent No. 2601532 and Japanese Patent Laid-OpenNo. 2008-68949, after the feeding operation is completed, the sheetsupporting plate is configured to be retracted from the feeding rollerbefore the feeding operation of the next sheet, so that a driving sourceand a driving transmission system for transferring a driving force arerequired. Therefore, the configuration becomes complicated, therebycausing an increase in cost and an increase in size.

Specifically, according to the feeding apparatus disclosed in JapanesePatent No. 2601532, the feeding motor for driving the feeding roller isconnected to the sheet supporting plate by a pinion and a rack. Then,when the feeding operation is performed, the feeding motor is forwardlyrotated, moves to a position where the sheet supporting plate comes inpress contact with the feeding roller, and after the feeding operationis completed, the feeding motor is reversely rotated, and the sheetsupporting plate moves to a position to be retracted from the feedingroller. In addition, a one way clutch is disposed between the feedingmotor and the feeding roller described above. By the operation of such aone way clutch, the feeding roller rotates to feed the sheet stacked onthe sheet supporting plate when the feeding motor is forwardly rotated,and does not rotate when the feeding motor is reversely rotated, so thatthe sheet stacked on the sheet supporting plate is not damaged.

In addition, according to the feeding apparatus disclosed in JapanesePatent Laid-Open No. 2008-68949, the sheet supporting plate with thestacked sheet comes in press contact with the feeding roller by a sheetsupporting plate pressing spring disposed in the moving portion which ismovable by being driven from an arbitrary driving source and applies thebiasing force. The above-mentioned moving portion is configured suchthat the sheet supporting plate moves to a first position where thesheet supporting plate is retracted from the feeding roller and nobiasing force is generated, and to a second position where the sheetsupporting plate comes in press contact with the feeding roller and thesheet stacked on the sheet supporting plate is fed. Furthermore, themoving portion is configured to move to a third position which is setbetween the first position and the second position. When the movingportion moves to the third position, the biasing force with respect tothe feeding roller of the sheet supporting plate is reduced according tothe amount of sheets stacked on the sheet supporting plate, and thesheet supporting plate is retracted from the feeding roller.

As described above, in Japanese Patent No. 2601532 and Japanese PatentLaid-Open No. 2008-68949, in order to configure the sheet supportingplate to be retracted from the feeding roller, the driving transmissionsystem such as a gear train or the driving source such as the motor isadditionally required. For this reason, in particular, as the feedingapparatus to be used in a low-end printer or a scanner of a small sizeand popular type, there are problems such that the configuration iscomplicated, the cost is increased, and the size is increased.

SUMMARY OF THE INVENTION

It is desirable to provide a sheet feeding apparatus having a simple andinexpensive configuration.

In order to achieve the above object, the invention provides arepresentative sheet feeding apparatus including: a stacking memberconfigured to be rotatably provided and to stack a sheet; a feedingmember configured to feed the sheet by rotating in a state of coming inpress contact with the sheet stacked on the stacking member; an elasticmember configured to generate a pressing force to make the sheet stackedon the stacking member come in press contact with the feeding member;and a restricting unit configured to abut on an uppermost sheet stackedon the stacking member and to restrict a position of the uppermost sheetto a position separated from the feeding member.

According to the invention, it is possible to provide a sheet feedingapparatus having a simple and inexpensive configuration.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the entire image formingapparatus which includes a sheet feeding portion.

FIGS. 2A and 2B are diagrams for describing the sheet feeding portionand a sheet cassette body.

FIGS. 3A and 3B are diagrams for describing a feeding operation when thesheet feeding portion of a first example is in a full load state ofsheets.

FIGS. 4A and 4B are diagrams for describing a feeding operation when thesheet feeding portion of the first example is in a light full load stateof sheets.

FIGS. 5A and 5B are diagrams for describing standby states when a sheetfeeding portion of a comparative example is in the full and light loadstates of sheets.

FIGS. 6A and 6B are diagrams for describing a sheet feeding portion of asecond example.

FIG. 7 is a diagram for describing a sheet feeding portion of a thirdexample.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the drawings. However, dimensions, materials,shapes, relative arrangement of components described in the followingembodiments may be suitably changed depending on a configuration orvarious conditions of the apparatus of the invention. Therefore, if nototherwise specified, there is no purpose of limiting the scope of theinvention only to these embodiments.

First Example

An image forming apparatus which includes a sheet feeding portion as asheet feeding apparatus according to the example will be described usingFIG. 1. Herein, a printer is exemplified as the image forming apparatus,which includes the sheet feeding portion to feed a sheet such as arecording sheet serving as a recording target. FIG. 1 is a schematiccross-sectional view of the image forming apparatus which includes thesheet feeding portion.

[Image Forming Apparatus]

In FIG. 1, an apparatus body 1 of the image forming apparatus and animage forming portion 1B which forms an image on a sheet such as arecording target sheet are illustrated. The sheet feeding portion as thesheet feeding apparatus is disposed below the image forming portion 1B.Further, the image forming portion 1B is provided with a laser scanner50, an image forming process unit which includes a photosensitive drum49 a as an image bearing member, and a transfer roller 49 b whichtransfers a toner image formed on the photosensitive drum 49 a onto asheet S.

Further, after the toner image formed on the photosensitive drum 49 a istransferred onto the sheet S by the transfer roller 49 b in the imageforming portion 1B, the toner image on the sheet S is fixed by a fixingdevice 51. Then, after the toner image is fixed by the fixing device 51,the sheet S are sequentially discharged and stacked onto a dischargetray 54 which is provided on the apparatus body.

The sheet feeding portion includes a sheet cassette 2 serving as a sheetstorage portion to stack and store the sheet, and a feeding roller 3serving as a sheet feeding member to feed the sheet S stored in thesheet cassette 2.

Furthermore, on a downstream side in the conveying direction of thefeeding roller 3, a separation roller 5 serving as a sheet separationmember is provided to come in press contact with the feeding roller 3,and a separation unit serving as a sheet separation portion is providedto separate the sheets S fed out of the feeding roller 3 one by one.Further, the separation roller 5 is pressed by a separation spring 24 inthe separation unit, and comes in press contact with the feeding roller3 by pressure of the separation spring 24, so that the sheets S can beseparated one by one.

Further, in the example, the sheet cassette 2 is guided and instructedby a guide (not illustrated) serving as a guide instruction portion, andis drawn out in the sheet conveying direction. In the sheet cassette 2,a sheet supporting plate 6 serving as a stacking member to stack thesheet S is provided to be rotated about a rotation center 11 in thevertical direction. Then, a sheet supporting plate spring 10 serving asan elastic member is disposed on the lower side of the sheet supportingplate 6. The sheet supporting plate spring 10 generates a pressing forceto make the sheet supporting plate 6 come in press contact with thefeeding roller 3.

In addition, the separation unit which includes the separation roller 5and the separation spring 24 is also provided in the sheet cassette 2.With such a configuration, when the sheet cassette 2 is detached orattached, the separation unit and the sheet supporting plate 6 is movedintegrally with the sheet cassette 2 in a state where the feeding roller3 is left in the apparatus body.

Herein, the uppermost sheet stacked in the sheet supporting plate 6 isrestricted in its position by a restricting unit 4 which abuts on theuppermost sheet to restrict the position of the uppermost sheet to aposition separated from the feeding roller 3. The restricting unit 4includes a sheet supporting plate auxiliary member 12 serving as arestricting portion and a cam 14 serving as a moving portion asillustrated in FIGS. 2A and 2B, and the detailed configuration will bedescribed below.

The feeding roller 3 is provided in the apparatus body to be rotated,and comes in press contact with an uppermost sheet S1 stacked on thesheet supporting plate 6 during a feeding operation and abuts on theseparation roller 5 on the downstream side in the sheet feedingdirection.

Then, in such a configuration of the apparatus body 1, when a signalindicating a sheet feeding start is transmitted from a controller unit(not illustrated), the feeding roller 3 receives a driving force of adriving motor (not illustrated) to be rotated in the counterclockwisedirection in FIG. 1. When the feeding roller 3 is rotated, the cam 14(see FIGS. 2A and 2B) disposed coaxially with the feeding roller 3 isrotated in synchronization therewith. As the cam 14 is rotated insynchronization with the rotation of the feeding roller 3, the sheets Sstacked on the sheet supporting plate 6 abut on the feeding roller 3,and the sheets S stacked on the sheet supporting plate 6 are fed by thefeeding roller 3. Thereafter, only the uppermost sheet S1 among the fedsheets S is separated from the other sheets by the separation roller 5and conveyed in a downstream direction.

Thereafter, the uppermost sheet S1 separated by one sheet passes througha pair of conveying rollers 16 along a conveyance path 46, and isconveyed to a transfer portion configured of the photosensitive drum 49a and the transfer roller 49 b through a pair of registration rollers48. At this time, a toner image visualized by a development device (notillustrated) is formed on the surface of the photosensitive drum 49 abased on a scanning laser beam output from the laser scanner 50. Thetoner image formed on the photosensitive drum 49 a is transferred ontothe conveyed sheet S1 by the transfer roller 49 b in the transferportion.

In this way, the sheet S1 transferred with the toner image is conveyedin the downstream direction, and the toner image is melt and fixed whilebeing heated and pressed by the fixing device 51. Thereafter, the sheetspass through a pair of conveying rollers 52 and a pair of dischargerollers 53 and are sequentially stacked on the discharge tray 54.

[Sheet Feeding Portion and Sheet Cassette]

FIGS. 2A and 2B are diagrams for describing the configurations of thesheet feeding portion and the sheet cassette 2. FIG. 2A is a diagramillustrating the entire sheet cassette, and FIG. 2B is an enlargeddiagram of mechanisms operated by the sheet supporting plate auxiliarymember 12 and the cam 14 to be described below.

In FIG. 2A, there are illustrated a sheet cassette case 2A and sideregulating plates 7 and 8 which restrict the end positions of the sheetin a direction (hereinafter, referred to as a width direction)perpendicular to the sheet conveying direction. A rear-end regulatingplate 9 restricts the rear end position of the sheet. These sideregulating plates 7 and 8 and the rear-end regulating plate 9 areprovided to slide in the sheet cassette body in order to restrict thepositions of end portions of various-sized sheets.

The sheet supporting plate 6 is disposed to be rotated by the rotationcenter 11 with respect to the sheet cassette case 2A, and receives apressing force (a pressing force) by the sheet supporting plate spring10 disposed on the lower surface of the sheet supporting plate 6 asdescribed above with reference to FIG. 1. In addition, on either side ofthe sheet cassette case 2A, the sheet supporting plate auxiliary member12 is disposed in each end in the width direction as a restrictingportion which is freely rotated about the same rotation center as therotation center 11 of the sheet supporting plate 6. The sheet supportingplate auxiliary member 12 is formed to restrict the upper surface of thesheet supporting plate 6 having the pressing force by the sheetsupporting plate spring 10, and includes a regulating roller 13. Theregulating roller 13 is held on the sheet supporting plate auxiliarymember 12 to be rotated, and at least two or more regulating rollers areprovided in the width direction of the sheet so as to support all typesof sheet stacked in the sheet cassette case 2A. In addition, the sheetsupporting plate auxiliary member 12 includes a cam follower portion 12a which abuts on the cam 14 at a position facing the cam 14 disposedcoaxially with the driving shaft of the feeding roller 3.

In addition, as described above with reference to FIG. 1, the separationroller 5 and the separation spring 24 which presses the separationroller 5 are integrally disposed in the sheet cassette 2. In otherwords, when the sheet cassette 2 is drawn out of the apparatus body 1,the sheet supporting plate 6 and the separation roller 5 retract fromthe feeding roller 3. Therefore, for example, the sheet stuck on a sheetconveyance path can be easily removed.

FIGS. 3A and 3B are diagrams for describing the feeding operation in astate where the sheet cassette is in a full load state of sheets. FIG.3A illustrates a standby state immediately before a feeding start signalis transmitted. FIG. 3B illustrates a state after the feeding operationstarts.

In FIGS. 3A and 3B, the sheet cassette 2 is in the full load state ofthe sheets S, the sheets S are stacked on the upper surface of the sheetsupporting plate 6, and the sheet supporting plate 6 is always pressedfrom the lower side toward the feeding roller 3 by the sheet supportingplate spring 10. The sheet S is always pressed toward the feeding roller3 by the pressing force from the sheet supporting plate spring 10similarly to the sheet supporting plate 6. Herein, a posture of thesheet supporting plate auxiliary member 12 is determined by theregulating roller 13 which abuts on the uppermost sheet S1 by the weightof the sheet supporting plate auxiliary member 12 itself. In otherwords, the sheet supporting plate auxiliary member 12 receives thepressing force indirectly from the sheet supporting plate spring 10through the sheet S, and thus is pressed toward the feeding roller 3.

Next, the cam 14 serving as the moving portion will be described. Thecam 14 is disposed coaxially with the rotation shaft of the feedingroller 3, and is rotated in synchronization with the rotation of thefeeding roller. Herein, the cam follower portion 12 a of the sheetsupporting plate auxiliary member 12 is located at a position facing thecam surface of the cam 14, and the rotation of the cam 14 causes thesheet supporting plate auxiliary member 12 to move. The sheet supportingplate auxiliary member 12 is provided to be rotated independently of thesheet supporting plate 6. The regulating roller 13 abuts on theuppermost sheet stacked on the sheet supporting plate 6 by the weight ofthe sheet supporting plate auxiliary member 12 itself, and the positionof the uppermost sheet is restricted to a position separated from thefeeding roller 3 through the regulating roller 13. The cam 14 makes thesheet supporting plate auxiliary member 12 rotate to restrict theuppermost sheet S1 stacked on the sheet supporting plate 6 to theposition separated from the feeding roller 3. In addition, when thefeeding roller 3 feeds the sheet, the cam 14 releases the position ofthe uppermost sheet S1 restricted by the sheet supporting plateauxiliary member 12 in order to make the uppermost sheet stacked on thesheet supporting plate 6 come in press contact with the feeding roller 3by the sheet supporting plate spring 10. As described above, since thesheet supporting plate auxiliary member 12 comes into contact with thesheet supporting plate 6 through the sheet S, the rotation of the cam 14causes the sheet supporting plate 6 to move.

[Feeding Operation of Sheet]

Next, the feeding operation of the sheet will be described. FIG. 3A is adiagram illustrating the standby state before the feeding starts. Asillustrated in FIG. 3A, the cam 14 abuts on the cam follower portion 12a of the sheet supporting plate auxiliary member 12, and stops in aphase where the sheet supporting plate 6 is restricted in a direction ofcompressing the sheet supporting plate spring 10. In other words, thecam 14 abuts on the uppermost sheet S1 stacked on the sheet supportingplate 6, and comes into contact with the sheet supporting plateauxiliary member 12, so that the sheet supporting plate auxiliary member12 is positioned to make the position of the uppermost sheet S1separated from the feeding roller 3. With this configuration, theregulating roller 13 having the sheet supporting plate auxiliary member12 abuts on the uppermost sheet stacked on the sheet supporting plate 6,and the sheet is retracted (separated) from the feeding roller 3. Adistance from the surface of the feeding roller 3 at this time to theuppermost sheet S1 is set to Lf. The position illustrated in FIG. 3A isa position at which the uppermost sheet S1 is separated from the feedingroller 3.

FIG. 3B is a diagram illustrating a state after the feeding operationstarts. As illustrated in FIG. 3B, the feeding roller 3 and the cam 14starts to rotate in a clockwise direction in the drawing and rotatablymoves to a phase where the positional restriction of the sheetsupporting plate 6 is released, so that the abutting of the cam 14 onthe cam follower portion 12 a of the sheet supporting plate auxiliarymember 12 is released. In other words, the cam 14 rotatably moves to aposition separated from the sheet supporting plate auxiliary member 12.Therefore, the positional restriction of the sheet by the regulatingroller 13 of the sheet supporting plate auxiliary member 12 is released.When the sheet supporting plate 6 is released from the restriction bythe regulating roller 13 of the sheet supporting plate auxiliary member12, the uppermost sheet S comes in press contact with the feeding roller3 by the pressing force of the sheet supporting plate spring 10. At thesame time, the sheet receives a conveying force from the feeding roller3 and fed out, and then conveyed to a separation nip formed by theseparation roller 5 and the feeding roller 3. One sheet among the sheetsS which reach the separation nip finally is separated by a separationpressure exerted on the separation roller 5 from the separation spring24, and then conveyed to the subsequent procedure.

Next, the feeding operation in a state where the sheet cassette is in alight load state of the sheets will be described using FIGS. 4A and 4B.FIGS. 4A and 4B are diagrams for describing the feeding operation in astate where the sheet cassette is in the light load state of the sheets.FIG. 4A illustrates the standby state immediately before a signalindicating the feeding start is transmitted. FIG. 4B illustrates a stateafter the feeding operation starts. Further, the operation is similar tothat of the full load state described using FIGS. 3A and 3B, and thedetailed description thereof will not be repeated. Herein, a differencebetween the full load state and the light load state will be described.

Comparing the light load state with the full load state of the sheets,the distance Lf described with reference to FIG. 3A and a distance Ledenoted in FIG. 4A are the same. In addition, the relation satisfiesLf=Le. This is because the position of the sheet supporting plateauxiliary member 12 is determined only by the phase where the cam 14 isstopped. In other words, it means that the position of the uppermostsheet S1 on which the regulating roller 13 abuts is not influenced by anamount of the sheets S stacked on the sheet supporting plate 6. In otherwords, no change of the uppermost position of the sheets S according tothe stacked amount means that the position of the sheet supporting plate6 stacked with the sheets S is changed according to the stacked amount.Further, similarly to FIG. 3A, the position illustrated in FIG. 4A is aposition where the uppermost sheet S1 is separated from the feedingroller 3.

Herein, a comparative example of the present example will be describedusing FIGS. 5A and 5B. In the comparative example, the cam 14 isconfigured to directly operate the sheet supporting plate 6 asillustrated in FIGS. 5A and 5B. FIG. 5A illustrates a standby positionat the time of the full load state of the sheets, and FIG. 5Billustrates a standby position at the time of the light load state ofthe sheets.

In the comparative example, as illustrated in FIGS. 5A and 5B, theoperation of the sheet supporting plate 6 becomes constant regardless ofthe stacked amount of the sheets S, and a relation of the distancebetween the feeding roller 3 and the uppermost position of the sheets Sbecomes Lf<Le. In the comparative example, a moving distance of thesheet supporting plate from the standby state before the feedingoperation at the time of the light load state of the sheets until thefeeding operation starts, and a time between the operations become largecompared to the full load state of the sheets. These increased distanceand time cause a collision noise between the sheet supporting plate andthe feeding roller at the time of the light load state of the sheets andan increase in operation interval, so that the flexibility of a sequenceis degraded.

Unlike the comparative example, according to the example, the cam 14pushes down the stacked sheets through the sheet supporting plateauxiliary member 12 and thus the sheet supporting plate 6 is operated.With this configuration, it is possible to constantly maintain adistance between the feeding roller and the uppermost position of thesheets regardless of the amount of the sheets stacked in the sheetcassette. Therefore, it is possible to constantly maintain the movingdistance of the sheet supporting plate from the standby state before thefeeding operation until the feeding operation starts, and a time betweenthe operations regardless of the stacked amount of the sheets.Furthermore, the collision noise generated by a difference in amount ofthe stacked sheets can be reduced and the varying operation interval canbe made to be constant, so that it is possible to contribute greatly tothe flexibility of the sequence. In addition, the above effects can beachieved through a simple and inexpensive configuration withoutrequiring a unique driving source.

Second Example

An image forming apparatus which includes the sheet feeding portionserving as a sheet feeding apparatus according to a second example willbe described using FIGS. 6A and 6B. The image forming apparatusaccording to the example has the same configuration as the image formingapparatus described in the first example except the configuration to bedescribed below.

FIGS. 6A and 6B are cross-sectional views illustrating main parts of asheet feeding portion according to the second example, in which FIG. 6Aillustrates the standby state immediately before a signal indicating thefeeding start is transmitted. FIG. 6B illustrates the state after thefeeding operation starts.

[Sheet Feeding Portion]

The sheets S are stacked in the sheet cassette 2, and the stacked sheetsS are disposed on the upper surface (sheet stacking surface) of thesheet supporting plate 6 which is rotatably provided. In a case where adistance of the sheet stacking surface on a side near the feeding roller(on the downstream side in the feeding direction) from the rotationcenter 11 is set to W and a distance of the sheet stacking surface on aside opposite to the feeding roller is set to Q, the sheet supportingplate 6 is configured to satisfy a relation of W<Q.

With the above configuration, since a barycentric position of the sheetsupporting plate 6 is inclined toward the sheet stacking surface of thedistance Q from the rotation center 11, the sheet supporting plate 6 isalways pressed toward the feeding roller 3 by a rotational inertiaforce. Similarly, the sheet S is also always pressed toward the feedingroller 3 by the rotational inertia force of the sheet supporting plate6.

Herein, the sheet supporting plate auxiliary member 12 is disposed to berotated about the rotation center coaxially with the rotation center 11of the sheet supporting plate 6, and the posture thereof is determinedby the weight of the sheet supporting plate auxiliary member 12 itself.In other words, the sheet supporting plate auxiliary member 12 isprovided with the regulating roller 13 such that the regulating roller13 is rotated by the weight of the sheet supporting plate auxiliarymember 12. Further, the regulating roller 13 is held in a state ofabutting on the uppermost sheet among the sheets S stacked on the sheetsupporting plate 6. In other words, the sheet supporting plate auxiliarymember 12 indirectly receives the rotational inertia force from thesheet supporting plate 6 through the sheet S, and pressed toward thefeeding roller 3.

Next, the cam 14 will be described. The cam 14 is disposed coaxiallywith the rotation shaft of the feeding roller 3, and is rotated insynchronization with the rotation of the feeding roller 3. Herein, thesheet supporting plate auxiliary member 12 is located at a positionfacing the cam surface of the cam 14, and the operation of the cam 14 istransferred to the sheet supporting plate auxiliary member 12. The sheetsupporting plate auxiliary member 12 is configured such that theregulating roller 13 abuts on the uppermost sheet stacked on the sheetsupporting plate 6 by the weight of the sheet supporting plate auxiliarymember 12, and thus restricts the position of the uppermost sheet to aposition separated from the feeding roller 3 through the regulatingroller 13. The cam 14 rotates (moves) the sheet supporting plateauxiliary member 12 to restrict the uppermost sheet S1 stacked on thesheet supporting plate 6 to the position separated from the feedingroller 3. In addition, when the feeding roller 3 feeds the sheet, thecam 14 releases the restriction on the position of the uppermost sheetS1 by the sheet supporting plate auxiliary member 12 such that theuppermost sheet stacked on the sheet supporting plate 6 comes in presscontact with the feeding roller 3 by the sheet supporting plate spring10. As described above, in order to make the sheet supporting plateauxiliary member 12 abut on the sheet supporting plate 6 through thesheet S, the cam 14 (that is, the sheet supporting plate 6) is operated.

In addition, the cam 14 is connected to the sheet supporting plate 6 bya sheet supporting plate tension spring 15. The sheet supporting platetension spring 15 is an elastic member to generate the pressing forcewith which the sheet supporting plate 6 comes in press contact with thefeeding roller 3. As described below, the sheet supporting plate tensionspring 15 does not generate the pressing force at the position where theuppermost sheet is separated from the feeding roller 3, but generatesthe pressing force to be large as the uppermost sheet moves from theposition separated from the feeding roller 3 until the uppermost sheetcomes in press contact with the feeding roller 3.

[Feeding Operation of Sheet]

Next, the feeding operation of the sheet will be described. FIG. 6A is adiagram illustrating the standby state before the feeding start. Asillustrated in FIG. 6A, the cam 14 abuts on the cam follower portion 12a of the sheet supporting plate auxiliary member 12, and stops in aphase where the sheet supporting plate 6 is restricted at a retractingposition from the feeding roller 3. In other words, the cam 14 abuts onthe uppermost sheet S1 stacked on the sheet supporting plate 6 and comesin contact with the sheet supporting plate auxiliary member 12 such thatthe sheet supporting plate auxiliary member 12 is located at a positionwhere the position of the uppermost sheet S1 is separated from thefeeding roller 3. In this way, the regulating roller 13 of the sheetsupporting plate auxiliary member 12 abuts on the uppermost sheet S1stacked on the sheet supporting plate 6 to retract (separate) the sheetS1 from the feeding roller 3. At this time, the tension spring 15connected between the cam 14 and the sheet supporting plate 6 isdisposed at a position where the spring pressure is not generated. Inother words, a force applied to the sheet supporting plate 6 toward thefeeding roller 3 in the standby state before the feeding correspondsonly to the rotational inertia force of the sheet supporting plate 6.Further, the position illustrated in FIG. 6A is a position where theuppermost sheet S1 is separated from the feeding roller 3.

FIG. 6B is a diagram illustrating a state after the feeding operationstarts. As illustrated in FIG. 6B, the feeding roller 3 and the cam 14start to rotate in a clockwise direction in the drawing, and rotatablymove to be a phase where the restriction of the sheet supporting plate 6is released, so that the abutment of the cam 14 on the cam followerportion 12 a of the sheet supporting plate auxiliary member 12 isreleased. In other words, the cam 14 rotatably moves to a positionseparated from the sheet supporting plate auxiliary member 12. With thisconfiguration, the positional restriction of the sheet by the regulatingroller 13 of the sheet supporting plate auxiliary member 12 is released.Furthermore, the tension spring 15 connected between the cam 14 and thesheet supporting plate 6 moves up to a position where a spring pressureis generated according to the rotation of the cam 14, and the sheetsupporting plate 6 comes in press contact with the feeding roller 3 bythe spring pressure of the tension spring 15. In other words, theuppermost sheet S1 stacked on the sheet supporting plate 6 comes inpress contact with the feeding roller 3. At the same time, the sheet S1receives the conveying force from the feeding roller 3, and is conveyedto the separation nip formed by the separation roller 5 and the feedingroller 3. One sheet among the sheets S which reach the separation nipfinally is separated by a separation pressure exerted on the separationroller 5 from the separation spring 24, and then conveyed to thesubsequent procedure.

With the above configuration, the sheet supporting plate 6 graduallyraises the pressing force in a process of abutting on the feeding roller3 according to the rotation of the cam 14 between a retraction position(see FIG. 6A) where no spring pressure is generated and an abutmentposition (see FIG. 6B). Therefore, it is possible to suppress a largecollision which may occur when the compressed spring is suddenlyreleased.

Further, the description herein has been made about the configurationwhere the cam 14 and the sheet supporting plate 6 are connected by thetension spring 15 and the spring pressure of the tension spring 15 isnot generated at the retraction position illustrated in FIG. 6A, but theinvention is not limited thereto. It is no matter that a weak springpressure is generated at the retraction position as long as the pressingforce is configured to gradually rise in the process of abutting on thefeeding roller 3 according to the rotation of the cam 14 between theretraction position illustrated in FIG. 6A and the abutment positionillustrated in FIG. 6B. Even in such a configuration, it is possible tosuppress a large collision generated at the time when the compressedspring is released.

As described above, by employing the configuration of the example, inaddition to the effect obtained in the first example, it is possible tomore reduce the collision caused in process of making the sheetsupporting plate come in press contact with the feeding roller, and thesheet feeding apparatus having a high silence property can be provided.

Third Example

An image forming apparatus which includes a sheet feeding portionserving as a sheet feeding apparatus according to a third example willbe described using FIG. 7. The image forming apparatus according to theexample has the same configuration as the image forming apparatusdescribed in the second example except the configuration to be describedbelow.

FIG. 7 is a cross-sectional view illustrating main parts of the sheetfeeding portion according to the third example, and illustrates a stateafter the feeding operation starts.

The sheet feeding portion according to the example includes a sheetsupporting plate auxiliary spring 25 instead of the above-mentionedconfiguration of the sheet supporting plate 6 of the second example. Thesheet supporting plate auxiliary spring 25 is disposed on the lower sideof the sheet supporting plate 6. The sheet supporting plate auxiliaryspring 25 is a biasing member which generates a biasing force to alwaysapply a force to the sheet supporting plate 6 toward the feeding roller3, and is an elastic member having a low pressure compared to the sheetsupporting plate tension spring 15. In the state where the sheetsupporting plate 6 is in the full load state of with the sheets S, thesheet supporting plate auxiliary spring 25 is set to the lowest value (apossibly low pressure of the spring pressure) of the spring pressureunder which the sheet supporting plate 6 is movable toward the feedingroller 3.

According to the example, compared to the above-mentioned secondexample, it is possible to reduce the collision generated in process ofmaking the sheet supporting plate 6 come in press contact with thefeeding roller 3 while applying a force to the sheet supporting plate 6toward the feeding roller 3 by the biasing force stabilized by thespring pressure, and the sheet feeding apparatus having a high silenceproperty can be provided.

Other Examples

In the above-mentioned example, the description has been made about thesheet feeding apparatus which is integrally provided with the imageforming apparatus, but the invention is not limited thereto. Forexample, the sheet feeding apparatus may be detachably attachable to beoptionally connected to the image forming apparatus, and the same effectcan be obtained by applying the invention to the sheet feedingapparatus.

In addition, in the above-mentioned example, the description has beenmade about the sheet feeding apparatus which feeds the sheet such as therecording target sheet, but the invention is not limited thereto. Forexample, even in a case where the invention is applied to the sheetfeeding apparatus which feeds the sheet such as a reading targetoriginal, the same effect can be obtained.

In the above-mentioned example, the printer has been exemplified as theimage forming apparatus, but the invention is not limited thereto. Forexample, the invention may be applied to another image forming apparatussuch as an image reading apparatus (for example, a scanner), a copyingmachine, and a facsimile machine, or other image forming apparatusessuch as a multifunction peripheral in which these functions arecombined. The same effect can be obtained by applying the invention tothe image reading apparatuses or to the sheet feeding apparatuses usedin the image forming apparatus.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-035117, filed Feb. 26, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A sheet feeding apparatus comprising: a stackingmember configured to be rotatably provided and to stack a sheet; afeeding member configured to feed the sheet by being rotated in a stateof coming in contact with the sheet stacked on the stacking member; anelastic member configured to generate a pressing force to make the sheetstacked on the stacking member come in contact with the feeding member;and a restricting unit configured to abut on an uppermost sheet stackedon the stacking member and to restrict a position of the uppermost sheetto a position separated from the feeding member.
 2. The sheet feedingapparatus according to claim 1, wherein the restricting unit includes arestricting portion which abuts on the uppermost sheet stacked on thestacking member and restricts a position of the uppermost sheet to theposition separated from the feeding member, and a moving portion whichmoves the restricting portion to restrict the uppermost sheet stacked onthe stacking member to the position separated from the feeding memberand releases the positional restriction of the uppermost sheet caused bythe restricting portion to make the uppermost sheet stacked on thestacking member come in contact with the feeding member by the elasticmember when the feeding member feeds the sheet.
 3. The sheet feedingapparatus according to claim 2, wherein the restricting portion isprovided to be rotated independently of the stacking member, and arotation center of the restricting portion is the same as a rotationcenter of the stacking member.
 4. The sheet feeding apparatus accordingto claim 2, wherein the restricting portion includes a regulating rollerwhich is rotatably provided and abuts on the sheet stacked on thestacking member.
 5. The sheet feeding apparatus according to claim 2,wherein the moving portion is provided coaxially with the feedingmember, and wherein the moving portion rotates in synchronization withthe feeding member to a position abutting on the restricting portion andto a position separated from the restricting portion in order to make arestricting portion abut on the uppermost sheet stacked on the stackingmember and locate the uppermost sheet to the position separated from thefeeding member.
 6. The sheet feeding apparatus according to claim 4,wherein the elastic member connects the stacking member and the movingportion, and generates the pressing force to be increased according tothe movement from the position separated from the feeding member of theuppermost sheet to the position coming in contact with the feedingmember.
 7. The sheet feeding apparatus according to claim 6, wherein thestacking member is configured such that a rotation center is positionedto make the center of gravity inclined in a direction abutting on thefeeding member, and is always pressed toward the feeding member by arotational inertia force.
 8. The sheet feeding apparatus according toclaim 6, wherein the stacking member includes a biasing member whichgenerates a biasing force to be always applied to the feeding member,and wherein the biasing member is an elastic member having a lowpressure compared to the elastic member.
 9. An image forming apparatuswhich forms an image in a recording target sheet, comprising: a sheetfeeding apparatus configured to feed the sheet, wherein the sheetfeeding apparatus includes: a stacking member which is rotatablyprovided and stacks the sheet; a feeding member which comes in contactwith the sheet stacked on the stacking member and rotates to feed thesheet; an elastic member which generates a pressing force to make thesheet stacked on the stacking member come in contact with the feedingmember; and a restricting unit which abuts on the uppermost sheetstacked on the stacking member to restrict a position of the uppermostsheet to a position separated from the feeding member.